[RFC PATCH 7/8] dt-bindings: Add bindings documentation for RISC-V idle states
Anup Patel
anup.patel at wdc.com
Sun Feb 21 04:37:57 EST 2021
The RISC-V CPU idle states will be described in DT under the
/cpus/riscv-idle-states DT node. This patch adds the bindings
documentation for riscv-idle-states DT nodes and idle state DT
nodes under it.
Signed-off-by: Anup Patel <anup.patel at wdc.com>
---
.../bindings/riscv/idle-states.yaml | 250 ++++++++++++++++++
1 file changed, 250 insertions(+)
create mode 100644 Documentation/devicetree/bindings/riscv/idle-states.yaml
diff --git a/Documentation/devicetree/bindings/riscv/idle-states.yaml b/Documentation/devicetree/bindings/riscv/idle-states.yaml
new file mode 100644
index 000000000000..3eff763fed23
--- /dev/null
+++ b/Documentation/devicetree/bindings/riscv/idle-states.yaml
@@ -0,0 +1,250 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/riscv/idle-states.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: RISC-V idle states binding description
+
+maintainers:
+ - Anup Patel <anup.patel at wdc.com>
+
+description: |+
+ RISC-V systems can manage power consumption dynamically, where HARTs
+ (or CPUs) [1] can be put in different platform specific suspend (or
+ idle) states (ranging from simple WFI, power gating, etc). The RISC-V
+ SBI [2] hart state management extension provides a standard mechanism
+ for OSes to request HART state transitions.
+
+ The platform specific suspend (or idle) states of a hart can be either
+ retentive or non-rententive in nature. A retentive suspend state will
+ preserve hart register and CSR values for all privilege modes whereas
+ a non-retentive suspend state will not preserve hart register and CSR
+ values. The suspend (or idle) state entered by executing the WFI
+ instruction is considered standard on all RISC-V systems and therefore
+ must not be listed in device tree.
+
+ The device tree binding definition for RISC-V idle states described
+ in this document is quite similar to the ARM idle states [3].
+
+ References
+
+ [1] RISC-V Linux Kernel documentation - CPUs bindings
+ Documentation/devicetree/bindings/riscv/cpus.yaml
+
+ [2] RISC-V Supervisor Binary Interface (SBI)
+ http://github.com/riscv/riscv-sbi-doc/riscv-sbi.adoc
+
+ [3] ARM idle states binding description - Idle states bindings
+ Documentation/devicetree/bindings/arm/idle-states.yaml
+
+properties:
+ $nodename:
+ const: riscv-idle-states
+
+patternProperties:
+ "^(cpu|cluster)-":
+ type: object
+ description: |
+ Each state node represents an idle state description and must be
+ defined as follows.
+
+ properties:
+ compatible:
+ const: riscv,idle-state
+
+ local-timer-stop:
+ description:
+ If present the CPU local timer control logic is lost on state
+ entry, otherwise it is retained.
+ type: boolean
+
+ entry-latency-us:
+ description:
+ Worst case latency in microseconds required to enter the idle state.
+
+ exit-latency-us:
+ description:
+ Worst case latency in microseconds required to exit the idle state.
+ The exit-latency-us duration may be guaranteed only after
+ entry-latency-us has passed.
+
+ min-residency-us:
+ description:
+ Minimum residency duration in microseconds, inclusive of preparation
+ and entry, for this idle state to be considered worthwhile energy
+ wise (refer to section 2 of this document for a complete description).
+
+ wakeup-latency-us:
+ description: |
+ Maximum delay between the signaling of a wake-up event and the CPU
+ being able to execute normal code again. If omitted, this is assumed
+ to be equal to:
+
+ entry-latency-us + exit-latency-us
+
+ It is important to supply this value on systems where the duration
+ of PREP phase (see diagram 1, section 2) is non-neglibigle. In such
+ systems entry-latency-us + exit-latency-us will exceed
+ wakeup-latency-us by this duration.
+
+ idle-state-name:
+ $ref: /schemas/types.yaml#/definitions/string
+ description:
+ A string used as a descriptive name for the idle state.
+
+ required:
+ - compatible
+ - entry-latency-us
+ - exit-latency-us
+ - min-residency-us
+
+additionalProperties: false
+
+examples:
+ - |
+
+ cpus {
+ #size-cells = <0>;
+ #address-cells = <1>;
+
+ cpu at 0 {
+ device_type = "cpu";
+ compatible = "riscv";
+ reg = <0x0>;
+ riscv,isa = "rv64imafdc";
+ mmu-type = "riscv,sv48";
+ cpu-idle-states = <&CPU_RET_0_0 &CPU_NONRET_0_0
+ &CLUSTER_RET_0 &CLUSTER_NONRET_0>;
+
+ cpu_intc0: interrupt-controller {
+ #interrupt-cells = <1>;
+ compatible = "riscv,cpu-intc";
+ interrupt-controller;
+ };
+ };
+
+ cpu at 1 {
+ device_type = "cpu";
+ compatible = "riscv";
+ reg = <0x1>;
+ riscv,isa = "rv64imafdc";
+ mmu-type = "riscv,sv48";
+ cpu-idle-states = <&CPU_RET_0_0 &CPU_NONRET_0_0
+ &CLUSTER_RET_0 &CLUSTER_NONRET_0>;
+
+ cpu_intc1: interrupt-controller {
+ #interrupt-cells = <1>;
+ compatible = "riscv,cpu-intc";
+ interrupt-controller;
+ };
+ };
+
+ cpu at 10 {
+ device_type = "cpu";
+ compatible = "riscv";
+ reg = <0x10>;
+ riscv,isa = "rv64imafdc";
+ mmu-type = "riscv,sv48";
+ cpu-idle-states = <&CPU_RET_1_0 &CPU_NONRET_1_0
+ &CLUSTER_RET_1 &CLUSTER_NONRET_1>;
+
+ cpu_intc10: interrupt-controller {
+ #interrupt-cells = <1>;
+ compatible = "riscv,cpu-intc";
+ interrupt-controller;
+ };
+ };
+
+ cpu at 11 {
+ device_type = "cpu";
+ compatible = "riscv";
+ reg = <0x11>;
+ riscv,isa = "rv64imafdc";
+ mmu-type = "riscv,sv48";
+ cpu-idle-states = <&CPU_RET_1_0 &CPU_NONRET_1_0
+ &CLUSTER_RET_1 &CLUSTER_NONRET_1>;
+
+ cpu_intc11: interrupt-controller {
+ #interrupt-cells = <1>;
+ compatible = "riscv,cpu-intc";
+ interrupt-controller;
+ };
+ };
+
+ riscv-idle-states {
+ CPU_RET_0_0: cpu-retentive-0-0 {
+ compatible = "riscv,idle-state";
+ riscv,sbi-suspend-param = <0x10000000>;
+ entry-latency-us = <20>;
+ exit-latency-us = <40>;
+ min-residency-us = <80>;
+ };
+
+ CPU_NONRET_0_0: cpu-nonretentive-0-0 {
+ compatible = "riscv,idle-state";
+ riscv,sbi-suspend-param = <0x90000000>;
+ entry-latency-us = <250>;
+ exit-latency-us = <500>;
+ min-residency-us = <950>;
+ };
+
+ CLUSTER_RET_0: cluster-retentive-0 {
+ compatible = "riscv,idle-state";
+ riscv,sbi-suspend-param = <0x11000000>;
+ local-timer-stop;
+ entry-latency-us = <50>;
+ exit-latency-us = <100>;
+ min-residency-us = <250>;
+ wakeup-latency-us = <130>;
+ };
+
+ CLUSTER_NONRET_0: cluster-nonretentive-0 {
+ compatible = "riscv,idle-state";
+ riscv,sbi-suspend-param = <0x91000000>;
+ local-timer-stop;
+ entry-latency-us = <600>;
+ exit-latency-us = <1100>;
+ min-residency-us = <2700>;
+ wakeup-latency-us = <1500>;
+ };
+
+ CPU_RET_1_0: cpu-retentive-1-0 {
+ compatible = "riscv,idle-state";
+ riscv,sbi-suspend-param = <0x10000010>;
+ entry-latency-us = <20>;
+ exit-latency-us = <40>;
+ min-residency-us = <80>;
+ };
+
+ CPU_NONRET_1_0: cpu-nonretentive-1-0 {
+ compatible = "riscv,idle-state";
+ riscv,sbi-suspend-param = <0x90000010>;
+ entry-latency-us = <250>;
+ exit-latency-us = <500>;
+ min-residency-us = <950>;
+ };
+
+ CLUSTER_RET_1: cluster-retentive-1 {
+ compatible = "riscv,idle-state";
+ riscv,sbi-suspend-param = <0x11000010>;
+ local-timer-stop;
+ entry-latency-us = <50>;
+ exit-latency-us = <100>;
+ min-residency-us = <250>;
+ wakeup-latency-us = <130>;
+ };
+
+ CLUSTER_NONRET_1: cluster-nonretentive-1 {
+ compatible = "riscv,idle-state";
+ riscv,sbi-suspend-param = <0x91000010>;
+ local-timer-stop;
+ entry-latency-us = <600>;
+ exit-latency-us = <1100>;
+ min-residency-us = <2700>;
+ wakeup-latency-us = <1500>;
+ };
+ };
+ };
+
+...
--
2.25.1
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